Spray applying of mold-release agent onto a mold for die casting has heretofore been effected by a spray head 11' mounted on the exterior of the mold with the mold opened as shown in FIG. 6. Some prior art method used a release agent spraying nozzle provided in the interior of a mold, but still it effected the spray applying with the mold open.
Since the prior art method spray applied a mold-release agent with the mold open, it was quite difficult to spray apply a mold-release agent selectively only to those portions of a mold which were contacted by molten metal such as aluminum and which were required to be covered with a release agent, such as lasting surfaces, sprues, molten metal wells, air vents and the like as will be hereinafter generally referred to as cavity section, so that the release agent was also applied to those portions of the mold other than the cavity section which were not required to be covered with release agent, such as parting surfaces of the mold and sliding surfaces of a movable mold insert. As mold-release agent was repeatedly spray applied to a mold, it gradually built up on those portions of the mold other than the cavity section. The thickness of the build-up of release agent itself or of aluminum tailings adhered to the sticky release agent formed gaps between the parting surfaces of the mold even when it was closed, so that molten aluminum flowed into such gaps to form flashes, resulting in the need for a deflashing step each time after the casting process. In addition, the increasing thickness of the release agent build-up and the adhered aluminum tailings caused unevenness in dimensions of last articles.
Furthermore, since mold-release agent was spray applied to the mold from the exterior thereof with the mold open, all of the release agent did not adhere to the mold, not only resulting in lower efficiency in the application of release agent and a relatively large loss of release agent, but also causing some surplus release agent to scatter around, thereby contaminating the surrounding environment.